In known elevator drives, these drives are operated with a converter which is appropriate for their power or rating. This means that one converter is used for one elevator drive, respectively. For relatively high elevator ratings, provision is at the moment made for a plurality of drives which are each operated by one or more converters, to act on one motor shaft, or for a plurality of drives to move the elevator independently of one another, at the same time, and adjacent one another.
Indeed, it should be noted that converters with an appropriate rating are required for both low and high ratings. In this case, the cost ratio for converter ratings above a specific rating (>100 kVA peak output rating) rises more than proportionally, thus additionally increasing the costs for elevators of more than a specific elevator rating.
However, the conventional procedure is also problematic in terms of the availability of the elevator. Particularly in the high-rating range, availability of the elevator should always be ensured. In the event of faults or failures which are caused by a defective converter, the elevator will come to rest. This is also the case, for example, if the motor winding fails.
If a plurality of drives are acting on one shaft, this leads to a major increase in the physical length of the drive unit and therefore in the space required for the drive. It is therefore necessary to provide additional space in the machine room in order to satisfy this increased space requirement. For this purpose, the drives must be specially synchronized and there is a risk of the shaft being driven non-uniformly along its length.